Stabilized radio circuits



Jan. 12, TT 3 1,841,281

STABILIZED RADIO CIRCUITS Filed March 15, 1927 3 Sheets-Sheet l PIE L1-INVENTOR +lara/d E E/l/off %:7 AT TO RNEY Jan. 12, 1932. H. F. ELLIOTT1,841,281

STABILIZED RADIO CIRCUITS Filed March 15, 1927 5 Sheets-Sheet 2 I mVENTOR Ham/d E f/fibf/ HIS ATTORNEY 1932- H. F. ELLIOTT STABILIZED RADIOCIRCIiITS Filed March 15, 1927 3 Sheets-Sheet 3 Opera flng Range. 550#500 K6 HIS ATTOR Y Patented Jan. 12, 1932 DELAWARE Application.meal/incurs, 1927; ser' ;'a1 no. '1 t5;tool

This invention relates toifradio frequency circuits, and especiallytoelectronic emission amplifier circuits of this type, utilized inconnection With telephone 'or telegraphic sig-' naling.

When electronic "emission devices are'utilized for radiofreq'uencyamplification, eertain deleterious eii'ectsare noted; This-can bemorereadily'explained when the nature and structure of such electronicemission devices are elucidated.

- Such devices usuallycomprise a plurality I of electrodes enclosed n anevacuated vessel.

One of the electrodes serves as a-source of electronic emission, andis'usually' in theforin of a filament heated by the passage'-=of anelectric current therethrough. This-;filament Y thus forms a cathode,from which electrons flovv in the space of the vessel to'the-plateelectrode, or anode that is keptata potential positive with respect tothe filament, as

' aplate or B batteryJ The space cur- (usuallyin the form of a grid)canbe-placed' so as to nfluence the electron emlssion, and;

rent'hetween the plate and filament thus flows through the externalbattery circuit. The function ofamplificationis' rendered possible bythe fact that the space-current is very sensitive to theelectrical'con-tlitions in the tube; For example, a control electrode 7the influence is a function 'of'th e potential mionicrepeaters-oramplifiers, the capacity i system to be unstable. especiallyat-the higher crate disturbing oscillations.

proposed to utllize some form of-dampin'g, such as-resistances, toprevent thcse' oscillations; and also,-to provide "so call'e'd neutral 1difi'erence between, it and the filaments} Thus .iinute variationsin'p'otential difference a pliedbetween the grid and filamentjc'an causeV comparatively large corresponding *variaeftect between the electrodes'may cause the fre uenciess; the in'stabilit'i is manifested b atendency for thetubeoib repeaterg'tofgen- It has been fsramnrznnnanrooiitouirsff ei 'ooarona'rron or izing ci'r'cuits vvhiclilarefiintendedto compensate (for such parasitlo coupling. The

V HAROLD F. ELLIOTT, OF PALQ'ALT QoALIEonmA, ssI NoR, 3Y essrenii/rnnrszI a e I TO nemoconronn'rronor. Annalee, Y on roan, N; f

dampingarrangementis"obviously imprac sharp tuning-j the neutralizingcircuits need accurate;adjustmentsg z It is .accordinglybne of:theobjects of my 7 tical becauseit introduces lossesthat prevent";

inventiontoiprovid'e' :a stabilizing scheme that Y overcomes these'dlsadvantages, and'to makeit possible to construct amplifier systems inf asimplemanner, thatdonot require suchiextreme delicacy in adjustment.

'It is another object of my'invention to make it possible to feedbackenergy from'the, out- I i put side to the input side-of such an:amplifier system, in :order ;to: reamplify the currents and theirvariations, and? yet without the dangenofthe feed-back (or,regeneratiofl as it is usually called) [becoming unstable and caus ngundesiredoscillationsr we r ,My-i ention possesses :many; otherta dtages,=and ha -other objects which maybe made more easily a parent froma considere tion of several embodiments-dimy invention. 1

For-this purpose lfhave shoyvn a fewforms 'in the' drawings:accompanying and' forming I partof thepresent' specification." I shallnow J "proceedeto describe-these formsrin detail,

which illustratethegenei'alprinciples of my inventionfibut it is tobeun'derfstood that this detailed description is not :tobettaken' in: a'lin'iiting sen se,- since theiscope; of my invention isbest definedbyth appended claims.

' Referring to the: drawings {Figures =1-to41inclu ive areiiwiringediaresonant circuit, discussed hereinafter.

p In Fig. 1:I"'shoW one stageionly of my amplifier system',r but' ofcourse-it is understood" that any" desired number can" be:.connected incascade, "so far as practicable Also, I. have indicatedmysystem asappliedlto therecepe tion of'radio signaling'energy, but-it is notlimited tothis field; ThusiI sliovv a conven' grams of fou'r embodimentsof mymvention. V v i FigJ5-is a reactance'diagram of aparallel sov'tionalf form ofpick up system, comprising nection 13; v tunable circuit.1 4, comprising antenna-'llgloading coil12,and=a groundconi ment 19externally of the tube 17 through the following output circuit; coil 23,coil 24,

minute signaling energy and causes it to affect a thermionic amplifiertube 17. For this purpose, one terminal of condenser 16 is co-n nectedto control electrode 18, and the other terminal to filament19. Thisfilament is arranged to be heated by electricalenergy, as from a battery20. The negative side of the filament 19 can be grounded, as indicatedat 21. e

The electrons from filament 19 flow to the anode or plate 22, which isjoined to the filapositive terminal of B battery 25, battery 25,filament 19. A by-pass condenser 26 can be shunted around battery25 topermit the radio frequency component of the output current to passaroundthe battery 25. The

. signaling impulses cause correspondingly large impulses of current inthis outputcircuit, which can be coupled to-:a succeeding stage in aWell-understood mannerto provide another stage of amplification. This isindicated by the placing of a tunable circuit ininductive coupled,relation with coil23;

. this circuit can affect a succeeding tube, such as 17 alreadydescribed, in a manner similar to that disclosed.

As thus far described, the system does'not made such that the capacitivecoupling between grid 18 and anode'22, tends to stabilize the system bycausing negative rather than positive feed-back. In order that theresultant negative feed-back may not result in a loss of amplification,and also in. order that reactive coupling between circuit 14 and circuit27 may be; reduced substantially to zero, thereby making the tuning ofeach independent of reactive effects due to tuning of the other, Iprovide means for balancing the system. i

To secure. this result, the high frequency component of the outputcurrent is caused to traverse a netv-zork of inductances and capacitles;for nstance, a C011 28, similar to C01l V 23, is in parallelptherewithas regards inductance 24, 'andis in inductiverelation with coil 23,.although not necessarily closely coupled therewith. Furthermore, equalcondensers 29 and 30 are placed in parallel relation with inductance 24,by being connected to that terminal of inductance 24 which is nearestthe batteryi25j the other terminals .in circuit 27 via coil 23 due tothe capacity effect between grid 18 and plate 22 is neutralized by thesubstantially equal and opposite electromotive force induced therein bycoil 28, which is symmetrically arranged with coil 23 with respect tothe coil of circuit 27. Asymmetrical system is thus brought about by thefact that the'condensers 29 and 30 have equal values, coils 23 and 28have the same self inductances, and the same mutual inductance with thecoil of circuit 27, and capacity 31 has the same value as the capacitybe tween grid 18 and plate 22. The effects of other parasitic couplingbetween the input and the output circuits may be reduced substantiallyto zero by properly arranging the battery wires and by providingsuitable shielding between the circuits, indicated diagrammatically bynumeral 32, all in the manner well understood by those versed in theart.

Nowconsidering the output circuit for the first-stage, it; is seen thatcoil 24 is in series therewith; and paralleling this coil are thetwobranches 2829 and 2330. By proper choice ofthe constants of coil 24and the equal condensers 29 and 30, it is easy to ensure that it and-itsparalleling branches will have a but due to the range of operation asindicated,

only a portion of the righthand branch is used. This portion indicates anegative reactance. Since theefiect of including such a circuit in theoutput side of the tube is the same'as introducing a capacitivereactance therein, there is no tendency to produce oscillations, and-thesystem is stable. Furthermore, circuit 27, having equal effect on coils23 and 28, which in turn are connected to a system of fully balancedcapacities, cannot react on the preceding stage through thecapacitycoupling in tube 17 V It is possible with this scheme to obtainsome regeneration without danger of losing stability, simply bycouplingcoil 24 to coil 15. It is foundthat if that be done, theregeneration increases as the frequency dc creases, since-the coil 24has its impedance reduced with the frequency. This is desirfrom eachother so far able in ensuring a substantially uniformde.gree'ofamplification for the Whole range of frequencies. i

. Another form of my'inventionis shown in Fig. 2. This form operatessubstantially like that of Fig. 1, and difiers therefrom only; in'a fewdetails. For example," coil 231is closely coupled to acoil 33 in. atunable circuit 34, which coil 33 is in series with the condenser branchof the tuned circuitj Furthermore, the common terminal of condensers29and 30 is directly connected to ground, and is not directlyconnectedto one terminal of coil '24. In both forms of Figs.,1ra:'1d 2,

the series circuit consistin ofithei two b branches 2328"and1293O isalso designed tobe resonant toa'frequency below the range of operationof the system, wherety; the reaction on the succeeding stage is alsocapacitive. Thus'the coupling of this circuit to the capacity branch ofcircuit 34 in Fig. 2 has the effect of adding a capacity in series tothe variable condenser-35 already present in thebranch. Substantiallythe same eflects as in the'two forms discussed canbe obtained-in theform shown in Fig. 3. In this figure, the antenna circuit 11'12.13" isarranged to afi'ect 'a tunable circuit consisting of coils 36 and 37,both coupled tocoil l2, fixedcondensers 43 and 44, and variablecondenser 88. Thetherinionic amplifier 39 has the three usual ele ments40, 41 and Y42. Its control electrode 41 connectsdirectly to oneterminal of con denser 38, while filament connects to. the commonterminal of-the pair of equal. condensers 48 and 44that arearranged inshunt to condenser 38. 1 The-filament also connects, by way of groundsand 51,.tvith the common terminal of coils '36 andf37,=which-are woundin the same direction. The output circuit is conventional, andincludesprimary 45 of a radio frequency transformer, the secondary .46 of whichforms one element of a tunable circuit 47 for affecting the succeedingstage. A neutralizing"circuit. extends from the plate to the lowerterminal of coil 37, and includes a capacity 48 whichis'equal to thecapacity between-grid 41 and plate 42. A shield 49 se yes to isolate thetwo stages as undesiredcouplings are concerned.

. it is well understood that whatever efiefct the inter-electrodecapacity has'toiiriduce an ,electroinotivc. force across coil 36 iscounterbalancedby the electromotive force-induced .in COll '3! due tothe neutralizing circuit from plate 42 to 0011 37.. I lnaccordance withI "in invention l'stabilizethis arran ement for the range of operatingfrequencies by'ineluding an inductance coil '52 in the connec' tion fromfilament 4O to'coils 36 and 37.} C battery 53 can also be provided .inthis connection if desired, There is-thus'aalpap allel circuit joined bythis coil,which;:in= eludes in one branch, condenser 43 andflcoileaees-es so opposite that there isnoreactivecoupling bet'weencircult 47and the input circuit wh ch includes coils 36 and 37." Furthermore, coil52 is made of suchivaluethat the parallel circuit comprising coil 52 andbranches36, 43 and I 775 belowtherange ofloperationfoii the system.

37, 44 which parallelit, has a' natural. period As in the otherforms,,this has the eflectlof stabilizing. the operation of the systemwith in thatrange. I

signed however, primarily toensure a sub- Fig..-4 I show a circuitthatissimilar inmost-respects to Figs. 1 and 2;.,it,.is de so Istantially equal amplificationfor an signals within the tuning range ofcircuits l4'and t.

v [The manner in which this is: accom.- pushed will, now .be descrlbed.The input I circuit of tube l7 1s the same as nrFigs- 1 and 2. Theoutputcircuit includes a coil 54 (that 1' is closelycoupled to another,equivalent coil 55 in the neutralizing circuit) coils 23fand a4s1ni1larin action to the same numbered coils in Fig.2, and battery 25. -Goi1s28and} 23neednct-be very closelycoupled togetherlf The succeeding stage2'Zjshould be symmetrically coupled to 23'and 28 as in=Figure7 and alsosymmetrically coupled to coils 54 and 55'.

This is'ne'cessai'y in order that the potentials induced in these coilsby currents in the coil of'circuit 27v maybe symmetrically distrib ,gice uted in the balance of thejsystem.

28 30 29 31 and capacity 18 22 is sym -I metrical; there is no'reactiyecoupling be-g tween circuit :14 and circuit 27. Further; 195

more, byproper choice ofconstants, the output circuit canbecaused tohave a substantially constant efiect on the nput?c1rcu1t,j, 1

whereby uniform amplificationv isjobtainedp and without instability,TlllSlS rendered posslbleby :the co1ls54and 55, which being 1;

in series with the rest ofthe system, have a :risingpositi e impedanceas the frequency in'creasesgyand to thfsls added the falling ne'gatiyeimpedance, of the-parallel system uni;

pling between the input and the output side, andbetween the stages.In'order to effect thisresult, thecoupling-bfcoils 54 and-55 v musthesuch as to'assist the'eitectfof thecouf ce i1 5. 23' and, 28; andtheir natural' period inust ystem;

nected'.

Thus analyzing-Fig, in detail, the four arms forming a closed ;c1rcu1tare formedthenetresult-i's asubstan- -.'constant impedance ascwellas,cou-;

also; be. outside the operating .;1-

parity and the. grid-plate capacity. The

- coils 28, are connected across the diagonal it between theentremitiesof capacities 29 and n OJ.

is connected across the other diagonal, and

that'the various capacities forming the bridge circuit is the same as ofFig. 1.

Due to the fact that the input circuit are properly propor ioned, theinput circuit cannot be affected by any potential difference that mayoccur across coils'23 and 28; and conversely, the input circuit cannotaifect these coils throughthe parasitic grid-plate capacity. Thus thestages of amplification are isolated one from another, and principallyby the aid of a capacity'bridge.

Theanalysis of Fig. 2' as regards the bridge The main difference is inthe mode offconnection of i coil 24, but this does not alter the bridgethe second and-t structure detailed in connection with Fig.1.

In Fig. 3, a similar bridge is formed, but slightly difierentlyarranged. The four arms forming a closed circuit are formed respectivelyby the grid-plate capacity; the second, by capacityrlS; thethird,bycapacity 44; and the f rth, by capacity d3. The grid 41 connectsbetween the first and fourth arms; thatis,between the grid-platecapacity and capacity The filament connects between capacities i l and43. Plate 42 con nects between the first and second arms; that LALLJU isbetween the grid-plate capacity and capacity-e8. 7 7 V The inputcircuit. 86-3'Z88 connects across one diagonal of the bridge; that is,one terminal connects between the first and fourth arms; andthe otherterminal between bird. The output coil l5 connects across; the otherdiagonal of the bridge; that is, one terminal connects between seccndarm48 and the first arm formed by the grid-plate capacity; and. theotherterminal connects between the third and fourth arms 44 and 43'. Asbefore, due to the proportioning of the capacities in the bridge, thepotential differences across the output coil 45 cannot affect the inputside; 7 and conversely, the input side cannot afiect the output sidethrough the grid-plate capacity.

In l i l the brid e arms are the. same as v. l D- l 1n Flg. 1, exceptthat in the second and third plate 22 is connected between the thirdandfourth arm; that re, between caarms, formed respectively by thecapacities 29, 30, there are respectively inclu ed the coupledcoils and54;. However, these arms are substantially entirely capacitive, theeffect of the impedances of the coils 55, 54,

.being small. The output circuit including coils 23, 28 aresubstantially across a diagonal of the bridge as before, by connectingacross condensers 29, 30.

I claim: 1. In an amplifying system, an electronic emission device,having a plurality of electrodes, an input circuit for said device, anoutput circuit for sand devlce, means associated with at least one ofsaid. two circuits to oppose the eifectof capacitive couplmg between theelectrodes, and means forming with sald associated means, a parallelresonant circuit the resonance period of which is below the range ofoperation of the system.

2. In an amplifying system, an electronic emission device having aplurality of electrodes, an input circuit connected to the inputelectrodes, an output circuit connected to the output electrodes, saidoutput circuit including a series inductance, aparallel circuitconnected to the inductance and forming therewith a circuit that isresonant at a frequency below the range of operation of the system, andanother circuit connecting one of the input electrodes and said parallelresonant circuit and arranged to neutralize the capacity effect betweentwo of the electrodes.

3. In an amplifying system, an electronic emission device, an inputcircuit for said device including a coil, an output circuit for saiddevice including a coil inductively coupled to the coil in the inputcircuit, and means whereby the efiect due to this coupling, upon theinput circuit is that of a capacity reactance within the range ofoperation of the system. I

2. in an amplifying system, an electronic emission device having aplurality of electrodes, an input circuit connected between the inputelectrodes, a parallel circuit having a capacitive and an inductivesection, and resonant at a frequency below the range of operation of thesystem, an output circuit connected between the output electrodes andincluding the inductive section, the capacit1ve branch including a palrof coupled coils inc one of which is also included inv the output;

circuit, and a circuit extending. from the other'of said coupled coilsto one of the electrodes of the input circuit and including a "capacityin series that is equivalent to the capacity between said one oftheelectrodes and an output electrode.

5. In an amplifying system, an electronic emission device, having anelectron emitting electrode, a control electrode and an anode,

an input circuit'connected between the electron emitting electrode andthe control electrode,*apa1r of equal inductance coils coupled'together,a pairof equal capacities conne'cted in tandem acrossboth coils inseries, a connectionbetween the anode and that terminal of one of thecapacities which is di-.

rectlyiconnected to one of .said inductance coils, a capacity betweenthat terminal of the other capacity which is directly connected to theother coil and the control elec-.

trode, said capacity being equal to the capac pair of coupled coils, thepair of equal capacthe input circuit.

of the input electrodes withthe ities, and'the last mentioned inductancecoil has a parallelresonance ata frequency below the range of operationof the system,

7. The combination as set forth in claim 2, in which the seriesinductance is-coupled to 8. The combinationas set forth in claim 2,

in which a close inductive coupling is pro-- vided betweenthe. circuitthat connects one 7 parallel circuit, and the output circuit. 7 V r 9.The combination as set forth in claim 4, in which ap'air of equalclosely coupled inductance coils are provided, one being in se-' ries inthe circuit that includes the capacity equivalent to the inter-electrodecapacity, g

emisslon'device having an electron emitting 10. The combination as setforth in claim' and the other in series in the output circuit.

' 5, in which a'pair of equal closely coupled inductance coils areprovided, one being in series 1n the connection between the anode andone of the capacities, and the other in series with the capacity that isequal 'to the capacity between the control electrode and the anode. r

11. An electrical amplifying system having in combination a plurality ofelectronic amplifiers arranged in cascade, circuits adjustable forresonance over a range of frequencies interconnecting said amplifiers,means for reducing reactive couplings between said resonant circuits tonegligible values including a parallel resonant circuit having afrequency below the range of operation of the system, and means wherebythe amplification of each of the amplifiers in the system is maintainedsubstantially constant over the range of frequencies covered by the adjustableresonant circuits.

12. In an amplifying system, an electronic emission device having inputand output electrodes; means forming with said device, a four armcapacity brldge, sald electrodes being each 001111601366].I'QSPGCtlYGbZtQ a corner of the bridge; an input circuit connectingacross a diagonal of the bridge; a circuit connecting across the otherdiagonal of the:

bridge; and means whereby a capacitive re-3 reactance being effectivebetween the input and output electrodes 13. In an amplifying system, anelectronic ,1 emlsslon device having input and output ele trodes, meansforming with the capacity be-i tween the electrodes a four armedcapacity bridge, an input circuit-connectedacross one diagonal of saidbridge, and acircuit connected substantially across the other diagonal QI of saidbridge, the said-latter circuit including a pair ofcoupled'coils, and a coil con-i necting-between said .pair of coils andan input electrode 14, In an amplifying system, an electronic em ssiondevice having an electron emitting electrode, an anode, and a controlelectrode; means forming with the interele'ctrode capacities of saiddevice, a four armed capacitive bridge, the electron emitting, electrodeand the control electrode being connected to diagonallyopposite-points,and the anode to one'oftheotherpoints of the bridge; and a otherdia'gonal, said circuit including acoil that carriestheoutput currentand SZlld coil of the system.

circuit connected substantially across the V 15. In an amplifyingsysteman electronic electrode, an anode, and a control electrode;

means formingwith the interelectrode ca-t pacities of said device, afour armed capaci-z tive bridge, the electron emitting electrode and thecontrol electrode being connected to diagonallyvopposite points,and theanode to n one of theother pointsof the bridge; a 'circuit including apai'r of coupled coils con nected substantially across the other diago--nal; and a coil connecting between the said coils and to theelectronemitting electrode;

16. The combination as set forth in claim 1 5,'in which there isincludedlanother pair of coupled coils, one in the arm of the bridgethat extends between the anode and the electron emitting electrode',an'dthe other in that arm whichextends betweenthe electron emittingelectrode and that point on the bridge to which none of the threeelectrodes connect.

17. The combination as set forth in claim 15, in which thereis includedanother'pair of coupled coils, one in the-armof the bridge that extendsbetween the anode and the 'electhe capacities and coils beingsoproportioned that a substantially constant reactive efi'cct is producedthereby between .the inputand the emission device, an input circuit forsaid de-' vice, an output circuit for saiddevice, said output circuitincluding a series inductance, andv a parallel circuit connected to said1nductance and forming therewith a circuit that is resonant at afrequency below the range of operation of the system,/sa1d lnductancebeing coupled to said input circuit.

' 19. In an amplifying system,;an electronic 7 emission device, an inputcircuit for said device, an output circuit for said device, said outputcircuit including an output impedance and a series inductance, and acircuit including capacity connected in parallel with said ii pedanccinductance and forming therewith a circuit that is resonant at afrequency below the range ofoperation of the system,

said inductance being coupled to said input circuit.

20. In an amplifying system, an electronic emission device having aninput circuit and an output circuit including an inductance, means forneutralizing capacitive coupling between the electrodes of said devicecomprising a coil coupled to said output induc-' tance and a capacityconnected between said. coil and saidinput circuit, and a circuitincluding capacity connected in parallel with said inductanceand coiland forming therewith a parallel circuit which is resonant at afrequency below the range of operation f the system.

21. In an amplifying system, an electronic emission device having aninput circuit and an output circuit including an inductance,

means for neutralizing capacitive coupling between the electrodes ofsaid device com prising a coil coupled to said output induc tance and acapacity connected between said coil and said input circuit, a pair ofcapacities in series connected in parallelwith said inductance and coil,and a connection between the common terminal of said capacities and thecommon terminal of said inductance and coil whereby two parallelresonant circuits are formed, each of said parallel circuits beingresonant at a frequency below the range of operation of the system.

22. In an amplifying system, an electronic emission device, an inputcircuit for said deviceincluding a coil, and an output circuit for saiddevice including-a coil inductively coupled to the coil in the inputcircuit, means whereby the effect due to this coupling upon the inputcircuit is that of a capacitive reactance within the range of operationof the system, and inductively reacting means in said output circuitwhereby uniform amplification over the operating range is obtained.

, 23. In an amplifying system, an electronic emission device having apluralityof electrodes,.'an input circuit for said device, an output.circuit for said device, means associated with at least one of saidcircuitsto oppose the effect of capacitive coupling between theelectrodes, means forming with said associated means a parallel resonantcircuit the resonant period of which is below the range of operationof'the system, and an inductive reactance in circuit with said parallelcircuit, the combined impedance of'said parallel circuit and inductivereactance providing substantially uniform amplification over theoperating range.

24. In an amplifying system, an electronic emission device having aninput circuit and an output circuit including an inductance, means forneutralizing capacitive coupling between the electrodes'of said devicecomprising a coil coupled to said output inductance and a capacityconnected between said coil and said input circuit, a circuit includingcapacity connected in parallel with said in ductance and coil andforming therewith a parallel circuit which is resonant at a frequencybelow the range of operation of the system, and an additional seriesinductance in said output circuit. r

25. In an: amplifying system, anelectronic emission device having aninput circuit and anoutput circuit including an'inductance, a circuitfor neutralizing capacitive coupling between the electrodes of saiddevice comprising a coil coupled to said output inductance a capacityconnected between said coil and said input circuit, a pair of capacitiesin series connected in parallelwith said inductance and coil, aconnection between the common terminal of said capacities and the commonterminal of said inductance and coil whereby two parallel resonantcircuits are formed, each of said parallel circuits being resonant at afrequency below the range of operation of the system, and a pair ofcoupled inductances one in said output'circuit and one in saidneutralizing circuit. In testimony whereof I have hereunto set my hand.v

" .HAR-OLD F. ELLIOTT.

